I also used that RAM. No problems, but I did see improvement by lots on my Mac Mini. For one, speed boost- everything more responsive, must less waiting. I suspect hard disk is thrashing less also.

Also, my shared graphics RAM went up to 512MB, and there is noticeable performance improvement in many 3D games even if it's still not liquid smooth.

Agreed. Sure, feels like loading time slower, but then you remember that Mac Mini uses 5400rpm laptop hard disk. That's the real bottleneck after you upgrade the RAM. I've done more tests and come to that conclusion.

Now if I can find a WD Scorpio Black, and find a shop that can do the HD change for me without voiding my warranty...

Dun feel like SSD is worth it, too expensive given the difficulty of replacing a HDD in a Mac Mini and the current lifespan of flash memory.